JP7009500B2 - Fluoropolymer-based powder coating - Google Patents

Description

INDUSTRIAL APPLICABILITY The present invention relates to a fluorinated acrylic thermoplastic composition, a powder coating made from such a composition, and a method for preparing the powder coating.

Background of the Invention A typical thermoplastic fluoropolymer powder coating is characterized by a degree of mechanical performance and surface roughness or "orange peel" associated with the finish. "Orange peel" can be reduced by various approaches. Although the resin melt viscosity can be reduced to counter the orange peel, the reduced melt viscosity generally adversely affects the mechanical properties of the coating, especially impact resistance, flexibility, and crack resistance.

A powder coating of polyvinylidene fluoride (PVDF) and a copolymer of vinylidene fluoride (VDF) containing at least 90% by weight VDF is disclosed in US 4,770,939. The PVDF-based resin disclosed in the patent for powder coating is according to ASTM D3835 and has a melt viscosity of 6-7 kilopores at 230 ° C. A small amount of low molecular weight acrylic polymer is required as a fluidity improver.

References US 5,177,150 disclose a powder coating formulated from PVDF characterized by a low melt viscosity of about 1-4 kilopores, claiming that the inclusion of a fluidity improver is unnecessary. There is. However, the powder coating composition requires cryogenic pulverization in order to obtain a powder having a small particle size (20 μm or less) at a high output.

Therefore, it is necessary to develop a powder coating composition exhibiting good mechanical properties and weather resistance by a simple manufacturing method that does not use a fluidity improver and does not require the use of liquid nitrogen in the grinding process. .. By using a composition made from fluorinated and acrylic polymers with a melt viscosity of less than 1 kilopoise, the powder coating is efficiently ground at room temperature while exhibiting good mechanical properties and excellent weather resistance. It was found this time to get.

U.S. Pat. No. 4,770,939 U.S. Pat. No. 5,177,150

First of all, the present invention
a. 50-95% by weight thermoplastic fluoropolymer, and b. A composition consisting of 5 to 50% by weight of acrylic polymer.
The present invention relates to a composition in which the fluoropolymer has a melt viscosity of less than 0.04 to 1 kilopoise (kP) as measured at 100 seconds ^-1 and 230 ° C. using ASTM D3835.

Another subject of the invention is the above compositions, at least pigments, and optionally UV absorbers, light stabilizers, matting agents, leveling agents, degassing agents, fluidizing agents, wetting agents, and impact modifiers. A powder coating composition comprising several additives selected from.

Another subject of the invention is a method for preparing a powder coating using the powder coating composition of the present invention.

Another subject of the invention is the coating obtained from the curing of at least one powder coating composition according to the invention.

Description INDUSTRIAL APPLICABILITY The present invention is described herein in more detail and without implicit limitation in the following description.

First of all, the present invention
a. 50-95% by weight thermoplastic fluoropolymer, and b. A composition consisting of 5 to 50% by weight of acrylic polymer.
The present invention relates to a composition in which the fluoropolymer has a melt viscosity of less than 0.04 to 1 kilopoise as measured with ASTM D3835 at 100 seconds ^-1 and 230 ° C.

Thus, the term fluoropolymer has at least one monomer in its chain selected from molecules containing vinyl groups that can be opened for polymerization and is directly attached to this vinyl group to at least one fluorine atom. , Means any polymer or blend of polymers containing at least one fluoroalkyl group or at least one fluoroalkoxy group.

Examples of monomers include vinyl fluoride; vinylidene fluoride (VDF); trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP). ); Perfluoro (alkyl vinyl) ethers such as perfluoro (methyl vinyl) ether (PMVE), perfluoro (ethyl vinyl) ether (PEVE) and perfluoro (propyl vinyl) ether (PPVE): perfluoro (1,3-dioxol); perfluoro ( 2,2-Dimethyl-1,3-dioxol) (PDD); Formula CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ X (X is SO ₂ F, CO ₂ H, CH ₂ OH, CH ₂ OCN) Or the product of CH ₂ OPO ₃ H); the product of formula CF ₂ = CFOCF CF ₂ SO ₂ F; or the product of formula F (CF ₂ ) _n CH ₂ OCF = CF ₂ (n is 1, 2, 3, 4). The product of); or the product of the formula R ¹ CH ₂ OCF = CF ₂ (R ¹ is hydrogen or F (CF ₂ ) _z , z is 1, 2, 3 or 4); The product of formula R ₃ OCF = CH ₂ (R ₃ is F (CF ₂ ) z-, z is 1, 2, 3 or 4); perfluorobutylethylene (PFBE); 3,3,3- Trifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene can be mentioned.

The fluoropolymer may be a homopolymer or a copolymer and may also contain a non-fluorinated monomer such as ethylene.

For example, fluoropolymers are selected from:
-Preferably homopolymers and copolymers of vinylidene fluoride (VDF) containing at least 50% by weight of VDF, wherein the commonomers are chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), trifluoroethylene (VF3). ) And tetrafluoroethylene (TFE) homopolymers and copolymers;
-Homopolymers and copolymers of trifluoroethylene (VF3); and-Chlorotrifluoroethylene (CTFE), tetrafluoroethylene (TFE), hexafluoropropylene (HFP) and / or ethylene units, and optionally VDF and / Or copolymers that combine residues of VF3 units, especially terpolymers.

Advantageously, the fluoropolymer is a polyvinylidene fluoride (PVDF) homopolymer or copolymer. Preferably, PVDF contains at least 50% by weight, more preferably at least 75% by weight, even more preferably at least 85% by weight. In one embodiment, the comonomer is HFP. In another embodiment, the comonomer is TFE.

Characteristically, fluoropolymers have viscosities in the range of 0.04 to less than 1 kilopoise as measured with ASTM D3835 at 100 s ^-1 and 230 ° C.

The term "acrylic polymer" is a homopolymer of methyl methacrylate, or a copolymer of methyl methacrylate (MMA) and at least one other monomer copolymerizable with MMA, these copolymers containing at least 50% by weight of MMA. Represents the copolymer contained. Examples of comonomer copolymerizable with MMA include alkyl (meth) acrylate, itaconic acid, (meth) acrylonitrile, vinyl versatate, butadiene, styrene and isoprene. Advantageously, the acrylic polymer contains by weight, preferably 5-15% C1 to C20 alkyl (meth) acrylate, which is preferably methyl acrylate and / or ethyl acrylate. The acrylic polymer may also be functionalized; that is, the copolymer contains a unit of MMA and a second comonomer in the following general form:

式中、
Ｒ_１は、Ｈ又はＣＨ３を表す；
Ｒ_２は、Ｈ、又は官能基が結合した１～２０個の炭素原子を含有する直鎖又は分岐アルキルを表す。ほとんどの場合、ヘテロ原子（炭素でも水素でもない原子）を含むこのような官能基の例には、カルボン酸、スルホン酸又は硫酸、ホスホン酸又はリン酸、ヒドロキシル基、エステル、ケトン、ケトエステル、アミド、ウレタン、チオール、シロキサン、フルオロアルキル、アセトアセテート、オキシラン；ビニルエステル又はエーテル、アリルエステル又はエーテル、アセチレン基、ジエン、マロネートなどのビニル型（ｖｉｎｙｌｉｃａｌｌｙ）不飽和基が挙げられる。

During the ceremony
_R1 represents H or CH3;
R ₂ represents H, or a linear or branched alkyl containing 1 to 20 carbon atoms to which a functional group is attached. Examples of such functional groups, including heteroatoms (atoms that are neither carbon nor hydrogen) in most cases, include carboxylic acids, sulfonic acids or sulfuric acids, phosphonic acids or phosphates, hydroxyl groups, esters, ketones, keto esters, amides. , Urethane, thiol, siloxane, fluoroalkyl, acetoacetate, oxylane; vinyl ester or ether, allyl ester or ether, vinylylly unsaturated groups such as acetylene group, diene, malonate and the like.

Particularly advantageous are acrylic copolymers containing 0.5-20% by weight of acid-functional monomers or anhydride derivatives thereof, such as:

式中、
Ｒ_３はＨ又はメチルを表し、又は無水物誘導体については、以下の形式の構造を表す。

During the ceremony
R ₃ represents H or methyl, or for anhydrous derivatives, represents a structure of the form:

式中、Ｒ_４及びＲ_５は同一又は異なり、Ｈ又はメチルを表す。官能性コモノマーの割合は、可能な官能基を含むアクリルポリマーの０～２５重量％、好ましくは５～２０重量％であり得る。

In the formula, R ₄ and R ₅ are the same or different and represent H or methyl. The proportion of the functional comonomer can be 0-25% by weight, preferably 5-20% by weight, of the acrylic polymer containing the possible functional groups.

According to the second subject, the present invention comprises the above-mentioned thermoplastic composition, at least one pigment, and optionally a UV absorber, a light stabilizer, a matting agent, a leveling agent, a degassing agent, and a flow. It relates to a powder coating composition comprising an agent, a wetting agent, and some additives selected from impact modifiers.

The powder coating composition contains one or more pigments. The pigment may be organic or inorganic. According to one embodiment, the pigment component may include titanium dioxide, or titanium dioxide in combination with one or more other inorganic pigments, with titanium dioxide occupying most of the combination. Inorganic pigments that can be used alone or in combination with titanium dioxide include, for example, silica; various colors of iron oxide; lead titanate; and various silicates such as talc, diatomaceous earth asbestos, mica, clay and basic silica. Contains lead acid acid. Pigments that can be used in combination with titanium dioxide include, for example, zinc oxide, zinc sulfide, zirconium oxide, lead white, carbon black, lead chromate, leaving and non-reefing metallic pigments, orange molybdenate, calcium carbonate and barium sulphate. Is done. It is advantageous that the pigment component is present in the powder coating composition in an amount of about 5 to about 30 parts by weight.

The powder coating composition can contain one or more additives that are not pigments. Examples of these additives are UV absorbers, light stabilizers, matting agents, leveling agents, defoamers, fluidizers, wetting agents, and impact modifiers.

The additive contained in the powder coating may be organic or inorganic. They can be used alone or in combination of two or more. Some examples of UV absorbers include benzotriazoles, oxalic acid diarylamides, and 2-hydroxybenzophenones. Suitable light stabilizers include, for example, hindered amines, hindered phenols, or combinations thereof, such as poly (alkanoylpiperidin alcohol), eg, oligomers of dimethyl succinate with 4-hydroxytetramethylpiperidineethanol. Some examples of matting agents include silica and wax. Examples of leveling agents include copolymers of VDF and HFP, ester gums, and silicon oils having a melting point below 130 ° C. Examples of degassing agents include benzoins. Examples of fluidizers include silica and fumed alumina. Silica can also be used as a wetting agent. The impact modifier may preferably be core-shell type.

The powder coating composition consists of particles having an average size in the range of 10-50 μm, preferably 15-30 μm.

Another subject of the present invention is a method for preparing a powder coating using the powder coating composition of the present invention, which comprises the following steps.
i. A step of preparing a mixture of the thermoplastic fluoropolymer, acrylic polymer, pigment, and optional additives by blending these components and then pelleting or sheet extruding the mixture;
ii. A step of pulverizing the pellets thus obtained at room temperature with a hammer mill to obtain a powder;
iii. Step of collecting powder using a sieve with an opening of 50 μm;
iv. The step of applying the powder to the substrate and then subjecting it to heat treatment to form a coating.

The powder coating composition of the fluoropolymer, acrylic resin and pigment is melt-mixed by extrusion such as a twin-screw extruder operating in the range of 160 ° C to 210 ° C. The extruded mixture is then either pelletized or extruded into a sheet by conventional techniques.

In the next step, the pellets are ground into powder according to conventional techniques, preferably by using a hammer mill. The obtained raw material powder is classified into a desired particle size by passing through a sieve of an appropriate size in the range of 10 to 100 μm, preferably 15 to 80 μm, more preferably 15 to 30 μm.

The powder coating according to the present invention can be efficiently pulverized into particles having an average size of 10 to 50 μm at room temperature without using the cryogenic technique of pulverization. This makes it possible to handle the pellets more easily and ensures a lower cost of the overall process.

The resulting powder is then applied to the substrate according to any means suitable for obtaining a uniform distribution of the powder. Static electricity application is a preferred method of application at a voltage between 25 and 100 V.

The substrate is selected from metals such as iron, aluminum and manganese, preferably made from aluminum. The surface of the aluminum substrate may be oxidized or chemically treated, but is preferably chromiumized for optimum adhesion to the powder coating according to the invention. The substrate can be coated with a primer such as an epoxy resin prior to coating with a fluoropolymer powder coating.

After application, the powder coating undergoes sufficient heat treatment to melt the powder coating. The temperature used must be higher than the melting point of the powder.

In one embodiment, the coating is baked at a temperature between 220 and 260 ° C. for a duration of 5 to 20 minutes. The coating and its substrate are then cooled by any suitable means.

In another embodiment, the heat treated coated substrate comprises immersing in boiling water for 4-6 hours.

Another subject of the invention is a substrate coated with the coatings defined above according to the invention. The coating thickness is preferably, but is not limited to, 30-1000 μm. The substrate can be used for applications such as curtain walls of skyscrapers, traffic signs, and outdoor units of air conditioners.

[Example 1]
52.5 wt% PMMA resin containing 90:10 methyl methacrylate and glutaric acid anhydride copolymer with a melt viscosity of 0.2 kP as measured at 100 seconds ^-1 and 230 ° C. according to ASTM D3835. % PVDF homopolymer is added. Also, 25% by weight of TiO2 is added to the mixture. The mixture is blended and pelleted in a twin-screw mixer operating in the range 160 ° C to 210 ° C. The pellets are ground directly in a hammermill at room temperature. The particle size distribution of the obtained powder is measured by a Microtrac 3000 device using water as a medium. This powder is electrostatically applied at 50 kV onto a base material of chromiumized aluminum. The panel is then baked at 250 ° C. for 15 minutes.

The coated panel is evaluated by the method shown in Table 1 below.

[Example 2]
The procedure is the same as in Example 1 except for the composition of the fluoropolymer. 47.5% by weight of the formulation remains a PVDF homopolymer with a melt viscosity of 0.2 kP as measured at 100 seconds ^-1 and 230 ° C. according to ASTM D3835, and 5% by weight is 100 seconds ^- according to ASTM D3835. It is replaced with a VDF / HFP copolymer having a melt viscosity of 25 kP as measured at ¹ and 230 ° C. The overall viscosity of the fluoropolymer phase is 0.9 kP (measured at 100 s ^-1 and 230 ° C. according to ASTM D3835).

[Comparative Example 3]
PVDF homopolymers with a melt viscosity of 6 kP as measured at 100 seconds ^-1 and 230 ° C. according to ASTM D3835 were used in place of 0.2 kP PVDF homopolymers and instead of MMA / glutaric acid anhydride 90/10 acrylic copolymers. The same procedure as in Example 1 was used, except that a copolymer of MMA and ethyl acrylate was used in.

[Comparative Example 4]
Same procedure as in Example 1 except that PVDF homopolymers with a melt viscosity of 3.5 kP measured at 100 seconds ^-1 and 230 ° C. according to ASTM D3835 were used instead of 0.2 kP PVDF homopolymers. It was used.

The evaluation results are shown in Table 2.

These data show that fluoropolymer viscosities of less than 1 kP (as in Examples 1 and 2) allow for better grindability relative to Comparative Examples 3 and 4. Small particle sizes can be achieved by milling at room temperature, which is a major advantage in terms of milling cost and productivity. It is interesting to note that in the compositions of Examples 1 and 2, the main imparting properties of the coating remain achieved.

Claims (15)

a. 50-95% by weight of one or more thermoplastic fluoropolymers, and b. A composition consisting of 5 to 50% by weight of acrylic polymer.
A composition in which the fluoropolymer has a melt viscosity of less than 0.04 to 1 kP as measured with ASTM D3835 at 100 s ^-1 and 230 ° C. The fluoropolymer is a homopolymer and copolymer of vinylidene fluoride (VDF) containing at least 50% by weight, and the comonomer is selected from chlorotrifluoroethylene, hexafluoropropylene, trifluoroethylene and tetrafluoroethylene. Homopolymers and copolymers; homopolymers and copolymers of trifluoroethylene; and residues of chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene and / or ethylene units, and optionally VDF and / or trifluoroethylene units. The composition according to claim 1, which is selected from a polymer that binds the polymer, particularly a terpolymer. The composition according to claim 1 or 2, wherein the fluoropolymer is a polyvinylidene fluoride (PVDF) homopolymer or a copolymer of vinylidene fluoride and hexafluoropropylene or tetrafluoroethylene. The acrylic polymer is a homopolymer of methyl methacrylate (MMA) or a copolymer of methyl methacrylate and at least one other monomer copolymerizable with MMA, wherein these copolymers contain at least 50% by weight of MMA. The composition according to any one of claims 1 to 3. A powder coating composition comprising the composition according to any one of claims 1 to 4, and also containing 5 to 30% by weight of a pigment. The powder coating composition according to claim 5, wherein the pigment is selected from titanium dioxide, iron oxide, lead titanate, and silicate. Claimed that the composition further comprises at least one additive selected from UV absorbers, light stabilizers, matting agents, leveling agents, defoaming agents, fluidizing agents, wetting agents, and impact modifiers. The powder coating composition according to any one of 5 or 6. The powder coating composition according to any one of claims 5 to 7, wherein the composition comprises particles having an average size in the range of 10 to 100 μm, preferably 15 to 80 μm, more preferably 15 to 30 μm. A method for preparing a powder coating using the powder coating composition according to any one of claims 5 to 8.
i. A step of preparing a mixture of the thermoplastic fluoropolymer, acrylic polymer, pigment, and optional additives by blending these components and then pelleting or sheet extruding the mixture;
ii. A step of pulverizing the pellets thus obtained at room temperature with a hammer mill to obtain a powder;
iii. The step of collecting the powder using a sieve having an opening of 50 μm;
iv. A method comprising the steps of applying the powder to a substrate and then subjecting it to heat treatment to form a coating. The method of claim 9, wherein the powder is electrostatically applied to the substrate at a voltage between 25 and 100 V. The method according to any one of claims 8 or 10, wherein the substrate is made of aluminum or aluminum chromiumized. The method according to any one of claims 9 to 11, wherein the heat treatment comprises baking the powdered substrate for 5 to 20 minutes at a temperature of 220 to 260 ° C. The method according to any one of claims 9 to 11, wherein the heat treatment comprises immersing the base material to which the powder is applied in boiling water for 4 to 6 hours. The method according to any one of claims 9 to 13, wherein the obtained coating has a thickness in the range of 30 to 1000 μm. A coating characterized by being obtained from the curing of at least one powder coating composition according to any one of claims 5-8.